Electronic integrated circuits are subject to reverse engineering, copying and theft of intellectual property rights. An integrated circuit with encrypted logic is designed to function correctly only when certain signals, representing key values, are provided as inputs. The key values are typically stored off-chip and read to on-chip registers or flip-flops during a power-on or boot-up sequence. The key values may be stored in E-fuses, for example. Without the correct key values the circuit will not function as designed, in that a given input may produce an incorrect output. However, such an approach is vulnerable to attack as the key values may be exposed to an attacker as they are read into the chip.